Non-Intrusive - no inheritance, no interface.. only pure-python-business code.

It is based on the techniques of system snapshotting and transaction journalling. In the prevalent model, the object data is kept in memory in native object format, rather than being marshalled to an RDBMS or other data storage system. A snapshot of data is regularly saved to disk, and in addition to this, all changes are serialised and a log of transactions is also stored on disk.